The present invention relates to a propulsion unit for a self-propelled vehicle such as an agricultural tractor.
According to the art, propulsion units are known in which some of the energy produced by an internal combustion engine is transformed into electrical energy, in order to improve the control of the latter. However, these units are characterized on the one hand by low performance levels and on the other hand by a limited speed range at which the arrangement can operate at full power.
Various systems are known in the art which allow the power to vary continuously. For example, for this purpose, hydraulic, electrical and steam systems advantageously can be used. In general, whenever the power is transmitted by xe2x80x9cfluidxe2x80x9d means, it is possible to regulate this power continuously. Since it is known that any power is transmitted at the expense of loss of the power itself (as a result of efficiency or performance levels which are always lower than a factor one) and moreover that the transition from one sort of power (e.g. mechanical power) to another sort (e.g. electrical power) also always is done at the expense of efficiency, it has been attempted to obtain solutions which, whilst permitting fine and continuous regulation of the power, have the consequence that a portion of the power produced by the internal combustion engine must be transmitted purely mechanically (for safeguarding the highest possible level of efficiency). Thus, it has been necessary to devise a form of interaction between those factors which can be finely and continuously controlled, such as the electrical power, with the portion of power which is always transmitted mechanically. To this end, it has been important to see how handling of a first flow of power, converted into electrical power, affects a second flow of power which, from the moment when it is generated at the internal combustion engine, until it is transmitted to the wheels of the vehicle, always continues to be mechanical.
It is an object of the present invention to provide a propulsion unit which can achieve the speed of travel of the vehicle selected by the driver in a continuous manner.
It is an advantage of this invention that a propulsion unit that can achieve the selected speed of travel in a continuous manner can be utilized on an agricultural tractor.
It is a feature of this invention that an agricultural tractor can be operable to regulate continuously the power to be transmitted to the wheels of the tractor.
It is another object of this invention that the operator of an agricultural tractor can elect to operate the tractor as an electric motor vehicle.
It is another feature of this invention that the portion of the power which continues to be mechanical, is conditional on the electrical fraction.
It is another advantage of this invention that this conditioning takes place without appreciable losses for low performance or load levels.
It is still another object of this invention to retain a mechanical fraction of the power which is transmitted to the wheels of the tractor with the highest possible efficiency level.
These and other objects, features and advantages are accomplished according to the instant invention by providing a propulsion unit for a vehicle, including a diesel engine and at least two electrical machines connected mechanically to a device for subdivision/re-combination of the powers delivered by the diesel engine and delivered or absorbed by said electrical machines in which the unit is configured so that in at least one interval of the ground speed of the tractor, the electrical fraction of the power delivered or absorbed by the said electrical machines is zero.